This invention relates to an improved bearing arrangement for supporting high speed rotating shafts. More specifically, this invention relates to a specific bearing configuration designed for use in turbochargers.
In a turbocharger, a turbine wheel and a compressor impeller are carried on a common shaft. The turbine wheel is received within a turbine housing for communication with exhaust gases from an engine, whereby the shaft is rotatably driven during engine operation. The shaft is supported by suitable journal bearings and thrust bearings within a center housing connected between the turbine housing and a compressor housing receiving the compressor impeller. The exhaust gas driven turbine wheel thereby drives the compressor impeller to compress charge air for supply to the intake of the engine, all in a well known manner.
The rotating shaft in a turbocharger is subject to being driven at relatively high rotational speeds, such as on the order of about 100,000 rpm. or more. Such rotational speeds require the use of precision bearing components together with an effective system of bearing lubrication. In this regard, lubricating oil is commonly pumped under pressure to the turbocharger center housing for supply therethrough to lubricate the shaft bearings to prevent excessive bearing heating and wear.
When operating at a high rotational speed, some turbochargers emit an audible whine or noise objectionable to some consumers. This is particularly true when the turbocharger is used in a domestic vehicle wherein the engine is designed for relatively quiet operation. This noise occurs primarily as a result of high frequency radial shaft excursion caused by imbalanced rotating components. It is desirable, therefore, to provide an improved turbocharger bearing design for reducing radial shaft motion at high speeds.
Turbocharger bearings in the prior art typically comprise a plain-type floating sleeve bearing having a circular cross-section for reception over the shaft of the turbocharger with limited clearance. During operation of the turbocharger, the turbocharger shaft rotates within the bearing, and the bearing sleeve rotates or floats within the turbocharger center housing at a rotational speed somewhat less than the turbocharger shaft speed, depending upon the inner and outer diameter bearing clearances. See, for example, U.S. Pat. Nos. 3,993,370 and 4,009,972. Other bearings have been proposed which attempt to improve lubrication between the shaft and the bearing by providing an enlarged radius over a portion of the bearing inner diameter for reception of lubricating oil. During operation, the rotating shaft tends to draw oil from the enlarged radius, and to pump that into the smaller clearances between the shaft and bearing. See, for example, U.S. Pat. Nos. 3,058,787 and 4,037,889. However, none of these prior art sleeve bearings have been found to be satisfactory in controlling or reducing high speed noise in automobile turbochargers.
A variety of sleeve-type bearing designs are available in the general prior art for limiting radial excursions of a high speed rotating shaft. One design approach comprises the provision of a plurality of arcuate ramps about the inner diameter of the sleeve bearing, wherein oil is supplied between the shaft and the bearing at or near the base of each ramp. See, for example, U.S. Pat. Nos. 1,495,660, 2,134,621, 3,680,932 and 3,722,965. Another design approach has been to provide a plurality of steps or lands formed on a common radius and separated by axially extending oil supply grooves. See, for example, U.S. Pat. Nos. 421,089, 1,376,094, 1,397,050, 3,167,362 and 3,941,437. However, many of these various bearing designs are limited to use with a shaft rotating only in a single direction. Accordingly, these bearings cannot be reverse mounted in a turbocharger center housing, and thus are compatable with modern turbocharger high production rate manufacturing criteria. Others of these bearing designs are bi-directional, but they have been found to be unsatisfactory in preventing shaft excursions to reduce generated noise in high speed turbochargers.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved floating sleeve bearing specifically designed for use in high speed turbochargers for limiting radial shaft excursions, and thereby also for limiting generated noise.